The invention relates to a pipe arrangement for geothermal probes, comprising at least two pipes having at least one layer surrounding a lumen, wherein one of the pipes functions as inflow pipe and the other pipe functions as backflow pipe and at least one of the pipes is produced at least partially from a non cross-linked polymer material.
Pipe arrangements of this type for geothermal probes are sufficiently well known from the existing prior art. These pipe arrangements are designed to absorb heat from the earth and/or to release heat to the earth.
The German Reference 202004007567 U1, for example, describes a geothermal probe to be installed in a borehole in the ground. This geothermal probe consists of an outer pipe, which forms an outside wall of the probe and is closed at the lower end, as well as an inner pipe extending inside the outer pipe, wherein the annular space between the outer pipe and the inner pipe and the space inside the inner pipe function as lines for a heat transfer medium. The outer pipe in that case is embodied as corrugated pipe, at least over most of its longitudinal extension.
Also known are pipe arrangements for geothermal probes, which consist of pairs of pipes that are provided at the lower end with a connecting elbow and/or a connecting piece. One of the pipes is used as a feed line while the other pipe serves as a return line. However, several such pipe pairs can also be used inside a borehole, which are provided at the lower end with one or several shaped parts as connecting elements.
The European Reference 0582118 A1 furthermore discloses a pipe arrangement consisting of long, parallel-extending plastic pipes that are connected at the lower end. For this, at least one top section is connected by welding or gluing and so as to be liquid-tight to at least two long, straight and parallel pipes, and is furthermore connected via at least one bottom part by welding or gluing to at least one of the straight pipes, so as to be liquid-tight.
A pipe arrangement is finally also known from German Reference 20202578 U1, which consists of pipes made from cross-linked polyethylene.
Furthermore known are pipe arrangements for geothermal probes, for which a pipe section is embodied helical, wherein this helical section can have a constant or changeable diameter.
Also known is the installation of these types of pipe arrangements for geothermal probes inside boreholes and the subsequent filling of these boreholes with material having a high heat-conductivity.
However, to ensure the operation of the pipe arrangement for geothermal probes for a long period of time, especially those made of non cross-linked polymer materials, the pipes can be used only up to specific operating temperatures of approximately 40° C. The non cross-linked materials used until now for pipe arrangements for geothermal probes furthermore have the problem of significant slow crack development, which can lead to a break in the pipe arrangement for geothermal probes during the operation, in particular caused by scoring and/or notching caused resulting from the transport, handling at the construction site, and installation in the borehole.The non cross-linked pipe arrangements according to prior art of pipes for geothermal probes have the serious disadvantage of not being resistant to concentrated loads. Contrary to the presently held belief, however, it must be assumed that concentrated loads will also act upon the installed pipe arrangements for geothermal probes. In contrast to representations shown in the prior art, the pipe arrangements for geothermal probes are definitely not installed centered inside the borehole and surrounded on all sides by a concrete/bentonite mixture, but always rest at least in part against the wall of the borehole.Furthermore—again contrary to presently-held believes and representations—it should not be assumed that the borehole wall is smooth, but that it is notched. As a result, concentrated loads will act upon the walls of the pipe arrangement for geothermal probes. Not enough consideration has furthermore been paid so far to the fact that following the installation of the pipe arrangements for geothermal probes inside boreholes, concentrated loads can also be exerted by falling rocks.
Finally, it has not been taken into consideration so far that pipe arrangements for geothermal probes are subjected to considerable alternating loads. Even during the heating operation at the start-up of the heat pump, rapid temperature fluctuations of approximately 10K appear quickly together with the associated heat expansions. These temperature changes can be as high as 40K during the heating and cooling operation. Especially during the continuous operation, these types of loads can result in the forming of cracks on the inside, arranged opposite the concentrated load, of the pipe arrangements for geothermal probes and can continue to grow until they result in a break.
To be sure, pipe arrangements for geothermal probes of cross-linked polymer material are resistant to concentrated loads and do not exhibit slow crack development, but they also have the problem that the butt-welding technique cannot be used when attaching the elements for connecting the pipe pairs. Thus, the production of a pipe arrangement of this type for geothermal probes is material-intensive and cost-intensive.